Collaborative Research: Reframing Notions of Wet vs. Dry Subduction: The Search for a Deep Fluid Signature in Subducted Continental Crust Using Coupled O, B, and Fe Isotopes

俯冲带不仅代表了地球表面和内部之间质量传递的主要机制，而且也是大多数大地震和重要火山活动的来源，这两者都对人类文明产生了戏剧性和直接的影响。俯冲带深处流体的存在、规模和性质无疑是地震和岩浆产生的重要因素，因此必须加以识别和表征。这项研究将有助于我们目前对俯冲带深部流体的认识，并有可能建立一种研究俯冲带深部流体的新方法。正如标题所示，它还将重新定义湿俯冲和干俯冲的概念，这可能为研究俯冲带过程的其他想法和方法打开大门。该项目将为不同群体的研究生和本科生提供培训和研究机会。在本地小学至高中学校举办的外展活动，会让未来的科学家接触最前沿的地球科学。在造山运动早期，被洋壳包围的小体积大陆地壳可能俯冲到超高压（UHP）深度并被挖出。这些小的大陆地壳俯冲块体可以保存大规模深俯冲流体交代作用的证据。该团队假设，位于喜马拉雅西北部的一个年轻的超高压地区——Tso Morari地块，代表了一个小的、早期俯冲的大陆块体，可能在俯冲带的超高压地区经历了交代作用。最近的研究进展已经带来了新的同位素和地球化学指标，可以在挖掘出的俯冲物质和弧岩浆中识别俯冲衍生流体和熔体的起源。特别是，预计硼在脱挥发流体中富集，在相应的寄主岩石中耗尽，硼同位素值提供了脱挥发程度的敏感指示。此外，铁同位素系统正在成为一种潜在的强有力的平板衍生流体性质示踪剂。该项目将把这些新指标与更成熟和传统的俯冲流体示踪剂结合起来，包括氧同位素、热力学和流体模型、岩体地球化学、特高压岩石和伴生蛇绿岩/杂岩的亚铁/铁比率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zones represent not only the main mechanism of mass transfer between the Earth's surface and interior, but also the setting for a majority of large earthquakes and a source of significant volcanic activity, both of which have dramatic and direct effects on human civilization. The presence, scale, and nature of fluids in deep portions of subduction zones are undoubtedly important factors in the generation of both earthquakes and magma, and therefore must be identified and characterized. This study will contribute to our current understanding of deep fluids in subduction zones, and potentially establish a new method for studying them. It would also, as the title suggests, reframe notions of wet versus dry subduction, which may open the door to other ideas and methods for studying subduction zone processes. This project will provide training and research opportunities for a diverse group of graduate and undergraduate students. Outreach activities at local GK-12 schools will expose potential future scientists to cutting edge Earth Science.Small volumes of continental crust surrounded by oceanic crust may be subducted to ultrahigh-pressure (UHP) depths and exhumed in the early stages of orogeny. These small, subducted blocks of continental crust can preserve evidence of large-scale, deep subduction fluid metasomatism. This team hypothesizes that the Tso Morari terrane, a young UHP locality in the NW Himalaya, represents a small, early-subducted continental mass that likely experienced metasomatism at UHP in the subduction zone. Recent advances have led to novel isotopic and geochemical proxies to fingerprint the origin of subduction-derived fluids and melts both in exhumed subduction materials and arc magmas. In particular, boron is expected to be enriched in devolatilized fluids and depleted in the corresponding host rocks with boron isotopic values providing a sensitive indication of the extent of devolatilization. Additionally, iron isotope systematics are emerging as a potentially powerful tracer of the nature of slab derived fluids. This project will combine these novel proxies with the more established and traditional tracers of subduction fluids, including oxygen isotopes, thermodynamic and fluid modeling, bulk-rock geochemistry, ferrous/ferric iron ratios on a suite of UHP rocks and associated ophiolite/melange from the Tso Morari.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.